Some common suggestions for making divinity candy include testing the sugar for a hard ball stage and not making divinity in humid hot weather. Divinity is commonly made at holiday time, but can be made any time of the year, depending on the weather.
Testing the sugar as it cooks for a hard ball can be a little time consuming, but since it can occur between 250 degrees and 266, it is a good idea to test. Drop a bit of the cooking sugar into some ice water and gather it into a ball with fingers. If the sugar stays in a ball form, then it is ready. The ball will be firm and sticky when pressed between fingers. This should be done quickly so that the sugar doesn't go past the ideal heat.
Since divinity is often made in December during the holidays, humidity isn't a problem for many areas around the country. In some areas, like the south, humidity is a problem year round. It is best not to make the candy if it humid outside, even if the air conditioner is running, the air will still be wet. The candy will not set in a wet environment.